The present invention refers to an assembly for a cylindrical drill pipe for different kinds of fluids, where the drill pipes are coupled together so as to form a long drill string.
It is widely known, that drill pipes can be assembled with a coarse thread. With such pipes it is possible to transport one fluid in the pipe, and such transport has until now been sufficient for the users on drilling rigs.
Recently, the need for transporting more than one fluid has developed, but assembling drill pipes with more than one channel for different kind of fluids has met some difficulties, as the threads often are worn differently and can never be tightened to a degree, where no leaks are present and at the same time secure, that the fluids are transported without being mixed through the proper channels in the pipes.
A pipe for more than one fluid is known from NO-B 169,797, where a main pipe is assembled using an internal lining in the joining of the main pipe, and an auxilary pipe is assembled next to the main pipe using locking and sealing rings. The assembly is held with external flanges connected to each other by bolts.
The surface of such connection is obviously not cylindrical or rotational symmetric around the centre axis and it is evidently not able to be used in a drill string, where the drill string is to be rotated during drilling operations.
In order to achieve a more smooth surface it is suggested in US-B 2,294,806 to connect external flanges with axially directed, xe2x80x9cinternal boltsxe2x80x9d being coun-tersunk with an opening sufficient for the service crew to turn the axially directed screws and thereby connect the pipes.
The subject matter of that publication is, however, not suited for being used in a drill string, as the assembly is not cylindrical and the flanges increases the diameter and thereby make the use of the drill string not feasable. Further, this technique is not suitable for transporting more than one fluid.
On this background it is the object of the invention to provide means for axially connecting drill pipes being able to transport separate fluids in a drill string.
To this end the inventions suggests that the connecting means are axially directed bolts inserted in the outer wall of the drill rod and extending axially past the end of the drill rod into internally threaded blind holes in the next drill rod to be connected to the first drill rod, and that each terminal surface of a drill rod is made with arrangements for at least one coupling means for the transport of different kind of fluids in the drill string.
With a drill pipe according to the invention it is possible both to connect drill pipes into one drill string without outer flanges and to transport different fluds in the drill string. Such fluids can be drilling mud for the drilling, brine, and e.g. hydraulic fluids. When assembling the drill rods to a drill string it is important that the connection according to the invention can be made without outer flanges or external auxilary pipes, as such protrusions would prevent the use of the drill string as a rotational device.
The prior art known from US-A-5299644 has only the axial directed bolts in common with the subject matter invention, as the bolts are arranged outside the circumference of the drill rods, i.e. not cylindrical shape. In addition, the tubular head exhibits different outer diameters and is far from cylindrical. Each of those two features will separately block the use of this prior art in a string of tubes, as the string can not rotate in the well because of the external bolts, and the tubular head with its larger diameters will stick in the well. Combining this prior art with the other cited prior art will still not solve the problem of providing means for axially connecting drill pipes being able to transport separate fluids in a drill string.
One preferred embodiment of the assembly for drill pipes can be found in, that the bolts are accessed through pocket openings in the outer wall of the drill rod in the proximity of the end of the drill rod, where the bolts are reaching into the internally threaded blind holes in the next drill rod, and that the pocket openings are of a width sufficient for screwing or unscrewing the bolts.
With such embodiment the assembly can be assembled manually under visual inspection of the assembly.
If the end surfaces of the drill rods are equipped with at least one guide pin and/or a corresponding recess, respectively, it will be easy to establish the correct connection and reduce the shearing forces on the bolts, and if the guide pins are shaped e.g. as truncated cones or tetrahedra with a cylindrical base portion, and the recesses each have a shape matching the guide pins, the connection can be performed with a greater precision in a faster way.
In another preferred embodiment of the flange assembly the coupling means for the fluids are made as coupling plugs provided with suitable sealing means. Thereby it will be possible in each assembling to choose, whether or not a fluid connection shall be established through the relevant fluid coupling.
In still another preferred embodiment of the flange assembly the bolts are actuated by one or more fluid motors in the drill rod. Thereby it can be advantageous that the fluid motors be driven from the other end of the drill rod, where suitable fluid couplings connect the fluid motors to a pressure source with regulating and surveillance means. With such embodiment it would not be necessary to mill the pocket openings in the distal wall of a drill rod.